Phytotoxicity of Cd and Zn on three popular Indian mustard varieties during germination and early seedling growth

Heavy metal toxicity is a major bottleneck to crop production throughout the world. India being a fast developing country is highly affected by heavy metal stress. Cd and Zn both pose great threat to crop production when present in excess. This work documents the differential tolerance of three cultivated varieties of Brassica juncea through physiological and molecular approaches at germination and early seedling growth. We observed that Zn doesn't inhibit germination whereas Cd does. But Zn effects the growth and development of the seedling after germination. Treatments of Cd (0, 0.5, 1.0, 2.0 and 4.0 mM) and Zn (0, 2.5, 5.0, 7.5 and 10 mM) doses were imparted in germinating mustard seeds. Seedling length, biomass (fresh and dry weight), metal tolerance index and chlorophyll content reduced in mustard varieties. The wrath of stress was more severe in Pusa agrani and less in Pusa bold under both Cd (2.0mM) and Zn (10.0mM) stress. The histochemical results showed H2O2, O-2, MDA, and cell death enhanced as dose was increased. Pusa agrani was the worst effected whereas Pusa bold the least. Various genes govern metal detoxification in mustards. Pusa bold showed better regulation in stress mediated abundance of genes depicting enhanced metal tolerance. It was found that among the three varieties Pusa bold was the most tolerant followed by Pusa bahar and Pusa agrani respectively. This is the first of its kind study where the effect of heavy metals has been studied and compared from molecular and varietal prospective at the germination stage.